芯

wick

padding

centering

mentally strong

dead center

dead center (of a baseball bat)

toilet drain outlet

to get to the heart of the matter

cardboard tube

Chinese water spinach (Ipomoea aquatica)

thick obi sash

lead pointer (for a clutch pencil)

spare pencil lead

lead of a pencil

wick of a candle

apple core

staple (for a stapler)

lamp wick

mechanical pencil lead

pencil lead case (for a mechanical pencil)

collar core (stiff fabric, etc. inside a collar)